As textile substrates age, their color tends to fade or yellow due to exposure to light, air, soil, and natural degradation of the fibers that comprise the substrates. As such, to visually enhance these textile substrates and counteract the fading and yellowing the use of polymeric colorants for coloring consumer products has become well known in the prior art. For example, it is well known to use whitening agents, either optical brighteners or bluing agents, in textile applications. However, traditional whitening agents tend to exhibit their whitening benefit upon deposition onto the textile substrate and in some instances even lose their effect over time.
Leuco dyes are also known in the prior art to exhibit a change from a colorless or slightly colored state to a colored state upon exposure to specific chemical or physical triggers. The change in coloration that occurs is typically visually perceptible to the human eye. Many of these compounds have some absorbance in the visible light region (400-750 nm), and thus more or less have some color. In this invention, a dye is considered as a “leuco dye” if it did not render a significant color at its application concentration and conditions, but renders a significant color in its triggered form. The color change upon triggering stems from the change of the molar attenuation coefficient (also known as molar extinction coefficient, molar absorption coefficient, and/or molar absorptivity in some literatures) of the leuco dye molecule in the 400-750 nm range, preferably in the 500-650 nm range, and most preferably in the 530-620 nm range. The increase of the molar attenuation coefficient of a leuco dye before and after the triggering should be bigger than 50%, more preferably bigger than 200%, and most preferable bigger than 500%.
Leuco dyes that deposit on textile articles during a wash can be triggered during drying, but may take some period before the color change manifests fully and the whiteness benefit becomes noticeable to the consumer. As such, there remains a need for a detergent composition that provides a consumer noticeable whitening benefit not only when the textile substrate is laundered, but also increases over time.
It has now surprisingly been found that the presently claimed combination of a plurality of whitening agents comprising leuco colorants provide the consumer with both an immediate whitening benefit upon laundering, and an increasing whiteness benefit over time.